The invention relates to a multilayer molded element suitable for bottom covering of vehicle floor areas or wheel housings. Molded elements of this type are utilized in order to protect the automobile body from whirled-up stones as well as spray water and in order to diminish the noise level in the interior of the vehicle and on the outside the vehicle.
When driving on gravel-paved streets and on wet roadways, stones and/or droplets of water are carried along by the tires and propelled at high speed against the vehicle body. On the one hand, this causes damage to the vehicle finish on the underside, so that corrosion may set in. In addition, the transfer of energy from the stones to the vehicle body leads to a broad-band, impulse-like vibration excitation (sound conducted through solids) of the vehicle body, which is radiated into the interior of the vehicle or outside of same in form of rattling—or crackling noise.
Hitherto customary facings of the wheel housing and the underfloor were typically made of plastic and essentially serve only for protecting the vehicle body from impacting stones. Due to the hard-surfaced solid construction, the vibration energy is not converted into heat upon the impact of the stones or water droplets, but is radiated as airborne sound either directly from the structural member or, after transfer of solid-borne sound, from the vehicle body. Other noises in the underfloor region, for example rolling motion noises or fume emission noises resulting from the exhaust train are reflected in undiminished fashion by the hard-surfaced facings.
A molded element of the here concerned type, serving as wheel house facing is known from U.S. Pat. No. 4,735,427. The layered construction comprises a dual layer, made of a layer of fibrous material and a plastic fiber layer. The two layers are needled together. Following joining by needles, the dual layer is molded by thermal deformation into a stable shell, adapted to the contour of the wheel housing. The plastic fiber/fibrous material dual layer shell, joined by means of needles, is, overall, relatively stable or hard after its deformation, so that it cannot optimally satisfy customer demands for more efficient noise reduction.